During the manufacture of elongated substrates, such as wires or cables, it is common to coat the wire or cable with an exterior thermoplastic coating. These exterior coatings can serve several purposes such as thermal and electrical insulation, corrosion protection and water blocking. The quality of the wire or cable is heavily dependent upon the quality of the exterior coating. If the coating is of inferior quality, uniformity or integrity, the performance of the wire or cable may be severely diminished. The characteristics of the coating are affected by both the coating material itself and the coating apparatus.
In more basic coating techniques, a continuous length of wire or cable simply passes through a heated slurry bath of coating material. As the wire or cable pass through the bath, the coating material adheres to the exterior of the wire or cable to provide the desired protective coating. The slurry bath technique, however, may yield marginally acceptable finished coatings, especially for those substrates requiring uniform and homogenous coatings. The slurry bath technique lacks the precise control needed to produce a consistent, high-quality coating on a substrate. The coating material in a bath may also be subject to increased contamination. Additionally, during an interruption in the manufacturing process, the wire or cable may not be easily removed from the heated slurry bath. As a result, temperature sensitive substrates may be damaged when exposed for extended periods to the bath.
In an effort to improve the quality of the coating on wires and cables, for example, coating systems have been designed with one-piece heated dies to apply the thermoplastic coating instead of a slurry bath. In such systems, a wire or cable is threaded and continuously moved through an aperture in the one-piece die. The coating material is then dispensed through the die and around the wire or cable. By employing a dispensing die, the amount or thickness of coating material applied to the substrate can be controlled in a precise manner.
The one-piece die coating technique, however, does have disadvantages. For instance, if the production line stops while the wire or cable is being coated, the wire or cable typically remains within the heated die. For temperature sensitive substrates, such as fiber optic cable, the continuous contact with the heated die may cause damage to the substrate itself. Additionally, one-piece dies do not provide for easy removal of the wire or cable. For instance, to remove the wire or cable from the one-piece die, one end of the wire or cable must pass through and exit the die. Although the wire or cable could be cut at the one-piece die to facilitate easier removal of the substrate from the production line, typical manufacturing techniques require the production of continuous rolls of wire or cable.
For at least these reasons, it would be desirable to provide a coating apparatus that would have the advantages of a one-piece die, but fewer disadvantages thereof. For example, it would be desirable to easily retract the die away from an underlying substrate, such as temperature-sensitive fiber optic cable, during a production interruption. Such a retractable dispenser system would also readily permit installation or removal of the wire or cable during the manufacturing process.